The invention relates to a laboratory apparatus for simultaneously carrying out reactions in a plurality of samples, which are arranged in an array.
A laboratory apparatus of this type can be, e.g., an apparatus for carrying out nucleic acid amplification procedures (hereinafter called PCR reactions), in which the quantitative formation of the amplification products (PCR products) during the PCR reactions is measured by optical means. This specific form of PCR is called real-time PCR reaction. The description hereinafter will focus mainly on PCR apparatuses of this type for illustration purposes without a limitation being intended.
It is common in real-time PCR reactions to measure mixed samples, which, for optical measuring purposes, contain fluorescence indicators that emit fluorescence signals after excitation by light of a suitable wavelength, whereby the intensity of the fluorescence signal depends on the quantity of PCR product formed. Usually, the increase of PCR products with progressing reaction time can be followed in real-time PCR reactions by means of an increase in the intensity of the fluorescence signals measured. However, measurements using transmission are also possible.
The technique of real-time PCR is described comprehensively in Neusser, Transkript Laborwelt no. 2/2000; “Echtzeit-PCR-Verfahren zur Quantifizierung von PCR-Produkten”. Reference shall thus be made to the content of this citation such that further explanations on possible fluorescence indicators and other aspects of this procedure are not required.
The plurality of samples that are processed simultaneously in laboratory apparatuses of this type, for example simultaneously undergo PCR amplification cycles, usually are arranged in an array. A thermocycler tempers the samples, e.g., to the various PCR temperature stages, e.g. using a temperature gradient in one or more of these stages. For observation and/or measurement of the quantitative development of PCR products formed, the laboratory apparatus of this type comprises an illumination device that emits light of suitable wavelength onto the samples. This light source can, e.g., be a blue or white light-emitting diode; other alternatives are, e.g., halogen lamps, xenon lamps, laser diodes, lasers, etc. Moreover, there may be provided additional optical components, e.g. in order to filter the illumination light or focus it onto the samples.
For measurement of the light signals, usually a fluorescence generated by the PCR products, a detector is provided that generates measured values in a manner dependent on a measured light intensity. It is also feasible to provide more than one detector. The detector can, e.g., be a CCD chip or a photo-multiplier or can contain a CCD chip or a photo-multiplier. The intensity of the light usually increases with the number of PCR products. However, procedures are known, in which the increase of PCR products is observed by means of a decrease of the fluorescence.
Furthermore, the apparatus usually also includes optical devices that define a beam path leading from the illumination device to the reaction samples and from there to the detector. These optical devices comprise, e.g., a dichroic mirror that is arranged between the illumination device and the samples and that allows the excitation light originating from the illumination device to pass to the samples and that reflects a fluorescence signal with a longer wavelength that is emitted from the optically-excited reaction region to the detector that is disposed, e.g., on the side. Usually, a number of other optical components are provided, for example filters, lenses, etc., which are upstream of the detector.
However, a fluorescence or a change of fluorescence will not be observable in all samples. If, e.g., the starting product to be amplified by means of PCR is not present in the sample at all, no fluorescence will be observed. However, in samples of this type it is not feasible to distinguish whether or not the lack of fluorescence truly originates from a lack of the starting product or if the excitation light source might possibly be defective, meaning that excitation of fluorescence never occurred. Both lead to the same result. In this context, it would be very important to be able to determine unambiguously why no fluorescence is observed, since real-time PCR measurements are used, e.g., in medical diagnostic work-ups. False diagnoses can have disastrous consequences.
An apparatus of this type is known from US 2003/0127609 A1 and includes a monitoring device that can monitor the functioning of the illumination device. This monitoring device consists of an additional light detector that is arranged such that illumination light is applied to it by the illumination light source. If this additional light detector determines that no illumination light impinges on it, the user is alerted to the fact that the illumination light source is defective.
It is considered to be a disadvantage of this solution that an additional costly detector is needed which, in addition, requires quite some space. The optical monitoring also appears to be failure-prone, e.g. because the absence of interfering light from any source other than the illumination device and interference-free impingement of the illumination light on the detector is required for correct monitoring. It is also considered to be disadvantageous that US 2003/0127609 A1 operates with a single illumination light source such that failure of the light source would render the entire device unusable. For selective illumination of a single sample of the plurality of samples, a mechanically complex relative motion between illumination device and samples is provided at this time. In the examples shown, a microtiter plate is moved mechanically, whereby the samples are contained in the receptacles of the microtiter plate.
The prior art also knows laboratory apparatuses that operate using more than one light source. WO 03/002991 A2, e.g., provides an arrangement of light-emitting diodes as illumination device. In this context, one light-emitting diode each is assigned to each of the samples. There is no monitoring of the light-emitting diodes for correct functioning such that in this case no unambiguous statement with regard to the cause can be made if there is no fluorescence.